With remarkable advances in computer and semiconductor technologies, electronic devices, such as media players, gaming devices, cellular phones, navigational devices, etc., have become more popular and affordable for most users. In the mean time, there is a prevailing trend for three-dimensional (3D) display in any of those electronic devices to provide the user a better visual enjoyment than traditional two-dimensional (2D) display.
In some navigational devices with so-called “three-dimensional” display, there is typically a two-dimensional overlay showing turns or maneuvers in a static, but detailed image. Such an approach requires the user to translate this two-dimensional view into the three-dimensional reality which they see through the windshield. This may cause confusion in routing situations where turns are closely spaced together with roads which are not part of the guidance route. For example, U.S. Pat. No. 6,285,317 to Ong discloses a navigation system for a mobile vehicle which incorporates a three-dimensional display updated with information from a wireless service provider. However, the three-dimensional display in Ong is simply a real environmental scene overlaid with a three-dimensional turn icon, as shown in FIG. 1.
Furthermore, U.S. Pat. No. 7,039,521 to Hortner et al. discloses a method and device for displaying driving instructions. More particularly, when calculating the perspective view from the viewpoint of the user, the inclination of the vehicle about its longitudinal and lateral axes relative to the road surface is taken into account, as is the incline of the road or the three-dimensionality of the terrain. However, as illustrated in FIG. 2, like Ong, Hortner discloses three-dimensional driving instructions overlaying on real-time images taken by a camera.
Conventionally, displaying road and polygon information over three-dimensional terrain poses difficult challenges. For example, the roads may “dig into” or “fly above” the terrain beneath them. In other words, if a long road segment crosses a hill or valley, it is very likely that the road no longer appears connected to the ground. The road may be under or over the terrain surface, which may cause visual discomfort for the user. One solution is proposed to dynamically generate roads which conform to the terrain below, over different Levels-Of-Detail (LODs). However, showing high level-of-detail terrain and roads requires large amounts of memory and processing capability.
Therefore, there remains a need for a method and apparatus to provide three-dimensional route guidance in a three-dimensional rendering environment with dynamic control of LODs without high computation requirements.